1. Field of the Invention
The present invention relates to a cracking tube with molded or shaped catalyst bodies for the catalytic cracking of process gases such as hydrocarbon gases, particularly natural gas, in elongated cracking tubes which can be heated from the outside and are closed at one end. The cracking tube contains a central inner tube for removing the process gases. The molded bodies are lined up along this inner tube.
2. Description of the Prior Art
These cracking tubes containing catalyst bodies are used for charging a tube cracking furnace with catalyst. They are frequently fastened at their upper end to a common carrier plate, are closed off at their lower end, and are heated from the outside with hot gases, for instance, with helium at about 950.degree. C. from a nuclear reactor cooling loop. In the chemical industry, cracking tubes with an inner tube are used in which the space between the inner tube and the outer tube is filled with numerous small molded catalyst bodies in a loose bed. These beds, however, cause a pressure loss or pressure drop of gas flowing through the beds, which pressure drop cannot be calculated with reasonable exactitude and is often different. In German Published Non-Prosecuted Application Nos. 19 46 741 and 25 07 937 approximately cylindrical molded bodies were proposed, which are lined up on the inner tube and have numerous axis-parallel openings for the passage of the process gases. In German Published Non-Prosecuted Application No. 25 07 937 an upper side of the one disc or washer fit the underside of the next washer, so that these washers are fixed with respect to each other in the circumferential direction. Thereby, the washers are secured against rotation.
In both cases, however, the desirable and necessary heat transfer from the inner tube to the process gas is disturbed because the latter is surrounded almost along its entire length by the central part of the molded body which has an insulating effect. In addition, in both cases, a non-uniform temperature and velocity profile develops over the cross section of the tube because the process gas of necessity flows faster at the hot outer tube. However, the temperature of the process gas should desirably be uniform in the furnace to effect more complete cracking or decomposition of the gas.